Reduction of Dinitrogen to Ammonia Catalyzed by Molybdenum Diamido Complexes

[Ar 2 N 3 ]Mo(N)(O- t -Bu), which contains the conformationally rigid pyridine-based diamido ligand, [2,6-(ArNCH 2 ) 2 NC 5 H 3 ] 2– (Ar = 2,6-diisopropylphenyl), can be prepared from H 2 [Ar 2 N 3 ], butyllithium, and ( t -BuO) 3 Mo(N). [Ar 2 N 3 ]Mo(N)(O- t -Bu) serves as a catalyst or precursor for the catalytic reduction of molecular nitrogen to ammonia in diethyl ether between −78 and 22 °C in a batchwise manner with CoCp* 2 as the electron source and Ph 2 NH 2 OTf as the proton source. Up to ∼10 equiv of ammonia can be formed per Mo with a maximum efficiency in electrons of ∼43%.